IM 743-1
11
Integration
Integrating the Modbus Communications Module into a BAS involves three steps:
Connecting the unit (node) to the network
Addressing and establishing communications with the unit
Configuring the unit to the building
Connecting to the Network
Network Topology
Standard Modbus network rules apply. The network is a daisy-chain of Modbus controllers including
all slaves and the master. The standard recommends that the network be terminated on each end with
the characteristic impedance of the network (about 120 ohms). Follow the guidelines stated in the
Modbus specifications (see Reference Documents section for details.)
Addressing and Establishing Communications
Network Address and Baud Rate
Valid slave nodes addresses are in the range of 0 – 247 decimal. The individual slave devices are
assigned addresses in the range of 1 – 247. A master addresses a slave by placing the slave address in
the address field of the message. When the slave returns its response, it places its own address in the
response address field to let the master know which slave is responding. Address 0 is the broadcast
address. When the address is 0, all slaves respond to the message.
The network address for a MicroTech II Chiller Unit Controller is set in the unit controller keypad
display. The Modbus network address and data transmission rate (Baud Rate) is only available in the
keypad/display when the protocol is set to Modbus. You must set the protocol, network address
(ident number), and baud rate before you can communicate on the Modbus network.
To set the protocol, network address, and baud rate on a unit controller:
1.
Navigate to the SET UNIT SP menus.
2.
Navigate down the SET UNIT SP menus to the Protocol = screen.
3.
Change protocol to Modbus. You must enter the Manager Password of “2001.”
Note:
Password screens listed are for Centrifugal Chillers. Passwords/screens for other
models may be different.
4.
Two more parameters appear in the screen: one for the network address (ID Number or Ident
No.) and one for the data transmission rate (Baud Rate).
Note:
See the appropriate Operation Manual for specific instructions for changing variables
with the keypad/display.
5.
Set the ID Number variable to the network address of the MicroTech II Chiller Unit Controller.
(See your network administrator for a network address.)
6.
Set the Baud Rate variable to the data transmission rate of the network.
Configuring the Unit Controller
The Modbus Communication Module and MicroTech II Chiller Unit Controller are configured
together at the factory. After you set up the network, the unit is ready to operate with the default
